Method for preventing condensation on handler board during semiconductor device testing

ABSTRACT

A semiconductor device tester and handler interface includes tester and handler boards with a coplanarity plate between them. The handler board includes a central area adapted to mount semiconductor devices to be tested by a tester. The tester board has tester contacts located to interface with a tester. During cold testing, to avoid condensation on the side of the handler board away from the devices being tested, dry gas is applied to the region formed by the coplanarity plate. During hot testing, flowing dry gas prevents the hot handler board from excessively heating the tester board and associated tester.

CONTINUATION INFORMATION

This is a divisional of U.S. patent application Ser. No. 08/914,915 filed Aug. 18, 1997, (now U.S. Pat. No. 6,118,286) which is a continuation-in-part of U.S. patent application Ser. No. 08/541,567 filed Oct. 10, 1995, now U.S. Pat. No. 5,705,932 issued Jan. 6, 1998.

FIELD OF THE INVENTION

The present invention relates to integrated circuit semiconductor device test apparatus, more particularly to a tester and handler board that provides for multiple site testing.

DESCRIPTION OF THE RELATED ART

Semiconductor device testing systems typically include a tester, which is an expensive piece of computing equipment for generating and receiving test signals, a chip handler, which is an expensive precise robot for moving semiconductor devices from one location to another under control of software, and a docking assembly for aligning and electrically connecting a tester mother board attached to the tester to a handler board attached to the chip handler. Typically, the tester mother board includes a plurality of compressible pins which must be accurately positioned to mate with contact pads or pin openings on the handler board. Sometimes the tester mother board and the handler board are combined, in which case the chip handler inserts semiconductor devices into the single board attached to the tester.

FIG. 1 shows the top view of a segment of a prior art standard automated test equipment (ATE) tester mother board 10. Mother board 10 includes an inner ring 11 and an outer ring 12 of spaced tester contacts. The rings 11 and 12 of tester contacts include groups of contacts such as groups 11 a and 12 a. Each group extends through the board to a male plug on the bottom surface of tester mother board 18, which is connected to pins of a tester. The tester pins receive signals from a computer. The tester mother board carries signals from the tester mother board to the handler board, and the handler board in turn carries the signals to a device under test. Output signals from the device under test are returned to the tester by a similar path. Tester contact groups 11 a and 12 a are repeated radially around the two concentric rings of tester contacts. Each group extends through mother board 10 to form an electrical contact in a plug extending downward from the bottom surface of mother board. These plugs must mate with pins in the tester. Ring 11 is spaced radially from ring 12 by a distanceD, which must match with a corresponding distance in the tester and thus may not be varied. Concentric rings 14 and 15 of compressible pins 14 a and 15 a such as pogo pins are provided radially inward of rings 11 and 12 of tester contacts 11 a and 12 a. Each of the pogo pins 14 a and 15 a is connected to an individual signal line in the tester. A third ring 16 of pogo pins 16 a are connected to the utility connections of the tester such as the tester's power supplies, relay controls, external +5 volt relay power supply, ground, and board statistics register. (A board statistics register contains information about the board such as its serial number, repair record, model number, and date of manufacture, and can be used by software to verify that the board is acceptable for the current use.) Threaded apertures 17 spaced around the tester mother board allow for connection to a handler board and for alignment of the two boards.

FIG. 2 is a schematic cross-sectional view of tester mother board 10 which shows the groups of tester contacts 11 and 12, the rings 14, 15, and 16 of pogo pins, and metallization lines 19 connecting contacts 11 and 12 to pins 14, 15, and 16. Individual pogo pins 14 a 15 a, 16 a and 16 b are also seen.

FIG. 3a illustrates the top surface 209 of a handler board 20 showing via connections 21 to selected pogo pins on the ring 16 of the mating tester mother board 10, metallization traces such as 22 a from contact pads such as 20 a to via connections 21, traces 22 b from via connections 21 to contact areas 23 adjacent to a test position 24 into which the semiconductor device will be inserted, mounted, and tested. FIG. 3a also shows a trace 22 c extending from a contact pad 20 a to a contact area 23 for holding a device to be tested. Bolts inserted through apertures 26 align handler board 20 with tester mother board 10 of FIG. 1 and hold the two boards together.

FIG. 3b is a bottom view of the handler board of FIG. 3a showing contact pads 27 which are contacted by corresponding pogo pins 16 a of ring 16 and showing the test site 24 for insertion of the semiconductor device under test. FIG. 3b also shows two rings of contact pads 28 and 29 which will be contacted by the pogo pins 14 a and 14 b of the two rings 14 and 15 of pogo pins, and shows alignment apertures 26. Typically, the screws that go through these holes are shoulder bolts to prevent loss during disassembly.

FIG. 4 shows another prior art mother board 30. Mother board 30 includes a test site 38 for inserting semiconductor devices and thus does not require a separate handler board. In FIG. 4, tester contacts 31 are arranged in groups which extend radially toward the center of mother board 30. A single test site 38 is positioned in the center of mother board 30 for receiving semiconductor devices for testing. The particular test site shown includes 48 sockets 39 for receiving 48 pins of a semiconductor device. Metallization traces connect the tester contacts to the sockets, one metallization trace for connecting each socket to a contact. For example, metallization trace 36 a connects contact 31 a to socket 39 a. In FIG. 4, 24 of the metallization traces are shown. Additionally, 24 more traces are formed in interior layers of mother board 30. Mother board 30 includes many more than 48 contacts 31. One mother board manufactured by Micro Ceramics, Inc. of Los Gatos, Calif., similar to mother board 30 includes 1152 contacts for interfacing with the SC212 tester from Credence Systems Corporation. Of these 1152 contacts, about half are connected to a ground plane in the board. Ground planes separate layers of metallization from each other. Some contacts are connected to two layers of power planes. Some are also connected to board statistics registers. About 300 contacts are available for carrying signals to a test site. But the space for test sites in such a mother board is limited to about 25% of the board area, and if the metallization traces are all to have equal delay, it is not possible to lay out 300 metallization traces in the area provided or to provide multiple test sites in the small area. Thus a board such as mother board 30 can not take full advantage of the tester with which it must interface.

FIG. 5 illustrates the interface of the tester mother board of FIG. 1 to an automated handler board or card 20 where the radial interior or central area of the ring 16 of pogo pins 16 a and 16 b (two pins shown) delineates a relatively small diameter working area W₁, in which a semiconductor device 25 can be mounted. This area, which is about 80-120 square centimeters in a typical handler board is so restricted in size that only a single semiconductor device 25 can be accommodated at one time on the handler board 20. Indeed, the area available for the device to be tested plus the metallization lines leading to the device may be less than 6% of the total area occupied by this prior art tester interface structure. Further, as can be seen in FIG. 1, the radial distance between the innermost ring 16 of pogo pins in tester mother board 10 and the group of tester contacts 12 is relatively long, actually about 12-15 cm in a typically utilized Credence, Inc. No. 8256 tester mother board. The prior art placement of the pogo pin rings 14, 15 and 16 radially inwardly of the groups 11 and 12 of tester contacts also limits the number of spaced pogo pins which can be accommodated around rings 14, 15, and 16 since the ring diameters are relatively small e.g., 12 cm for ring 16 in a Credence No. 8256 tester mother board. The above prior art configuration was designed to have the rings of pogo pins 14, 15 and 16 as close as possible to the semiconductor device test position 24 so as to minimize the length of metallization lines from the contact areas 23 to the pogo pin rings 14, 15, 16, and hence minimize any signal loss. However, FIG. 5 illustrates the radially wide separation of inner ring 16 of pogo pins in tester mother board 10 and contact areas 23 in handler board 20 from the tester contacts 11 and 12 which send and receive the test signals.

A need has arisen to permit a tester/handler to test multiple semiconductor devices at the same time on the same tester/handler, while minimizing any signal loss, and without necessitating any change in the spacing and location of the groups of tester contacts in order to be compatible with standard ATE testers. There is also a need for a handler board which can apply a larger number of signals to a single semiconductor device. As the tester mother boards become larger to accommodate higher and higher pin counts, a need has also arisen to ensure equal compression of all the pins on the tester mother board and to minimize any bending or buckling of the board. There is also a need to accommodate testing semiconductor devices at low temperatures.

SUMMARY OF THE INVENTION

In accordance with the present invention, a tester and handler interface is provided in which the tester mother board includes at least one ring of spaced electrical connectors positioned between the first and second groups of tester contacts on the tester mother board.

This permits the test sockets to be closer to the tester contacts, and greatly increasing the work area of the board. The board can include multiple sites for mounting and testing semiconductor devices. This in turn increases throughput of tested semiconductor devices without the purchase, set-up and use expense of additional testers, without additional facility space for additional testers and handlers.

In one embodiment of the invention, one ring of pogo pins connects to tester channels and another ring of pogo pins connects to the tester's utilities such as power supplies, relay controls, external +5 volt relay power supply and board stat register. The two larger rings of the invention can take the place of three or four rings used in prior art interfaces.

In another embodiment, a non-electrically conductive coplanarity plate shaped as a ring extends between the handler and tester boards. The coplanarity ring has an inner periphery bounding the central working area of the handler board and an outer periphery adjacent to the inner ring of pogo pins. The coplanarity ring functions to equalize the compression of the spring-biased pogo pins and prevents bending or buckling of the two boards without overstressing the spring-biased pogo pins. This coplanarity ring also assists in assuring a coplanar alignment between the tester and the automated semiconductor device handler which inserts semiconductor devices into the handler board.

During low temperature testing, the low temperature of the devices under test can cause condensation to form on parts of the handler board near the chips. This condensation can cause shorting between physically close metallization lines in the vicinity of the chips, particularly on the back side of the handler away from the chips, which may be in an environment different from the chips. To avoid moisture condensation during reduced temperature testing, the coplanarity ring may nearly seal the space between the tester and handler boards and thus form the wall of a container for dry gas, and may have radial or other grooves to allow venting of external dry gas pumped into the space between the tester and handler boards during such testing.

In yet another aspect, guide pins are provided on the tester mother board onto which both the handler board and the coplanarity ring are passed to align the interface and insure against improper mounting.

In one embodiment, a single board includes multiple metallization layers and can allow test sites to be located directly above tester contacts without interference. Thus there is sufficient space for multiple test sites. Alternatively, this multi-layer board can provide signal paths that cross each other to arrive at contact points on an upper surface of the board and leave a large area into which another board or other structure can be attached.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a segment of a prior art tester mother board.

FIG. 2 is a schematic side view of the prior art tester mother board of FIG. 1.

FIG. 3a is a top view of a segment of a prior art handler board.

FIG. 3b is a bottom view thereof.

FIG. 4 is a prior art board which interfaces with both a tester and a handler.

FIG. 5 is a schematic side view of a prior art interface including the mother board of FIG. 1 and handler board of FIGS. 3 and 4.

FIG. 6 is a schematic side view of a tester mother board of the invention.

FIG. 7 is a schematic side view of the interface formed by mating of the tester mother board and handler board of the invention.

FIG. 8 is a top view of the tester mother board of the invention with a mounted coplanarity plate.

FIG. 9 is a schematic top view of a segment of the tester mother board of FIG. 8.

FIG. 10 is a schematic bottom view of a handler board of the invention.

FIG. 11 is a top view thereof.

FIG. 12 is a bottom view of the coplanarity plate of the invention.

FIGS. 13a and 13 b are alternative side views thereof.

FIG. 14a is a top view of another tester mother board of the invention.

FIG. 14b is a coplanarity ring used with the tester mother board of FIG. 14a.

FIG. 14c is a bottom view of a handler board used with the tester mother board of FIG. 14a.

FIG. 14d is a top view thereof.

FIG. 15 is a top view of a tester mother board in a linear embodiment of the invention.

FIG. 16 is a coplanarity plate used with the tester mother board of FIG. 15.

FIGS. 17 and 18 are cross sectional views of an interface structure including the tester mother board of FIG. 15, coplanarity plate of FIG. 16, and a handler board.

FIGS. 19a and l9 b are bottom and top views respectively of a handler board usable with the tester mother board of FIG. 15.

FIGS. 20 and 21 illustrate two structures for electrically connecting metal traces in different metallization layers of a multi-layer printed circuit board.

FIGS. 22 and 23 show side and top views, respectively of representative electrical paths from a tester contact to a test socket.

DETAILED DESCRIPTION

FIG. 6 illustrates one embodiment of the tester mother board 40 of the invention. Tester contacts 41 and 42 have the same spacing and radial position as the two groups of tester contacts 11 and 12 in FIG. 1, so as to be compatible with standard automated test equipment. In contrast to the prior art, two rings 43 and 44 of spaced electrical connectors such as pogo pins 43 a and 44 a are positioned toward the outer periphery 46 of the tester mother board. Preferably, the rings of pins are positioned between the groups of tester contacts 41 and 42. A central area W₂ is formed which in one embodiment has an overall area of about 1000-1400 cm², which is about 10 times the area of the prior art central area W₁. By making the rings of electrical spring-biased pogo pins or connectors of larger diameter, the test interface can be made electrically smaller, i.e. shorter spans of metallization result when the semiconductor devices are placed physically closer to the metallization lines which carry test signals to and from their respective semiconductor devices.

FIG. 7 shows the enhanced working area W₂ of the interface (the mother board and handler board combination) as well as a non-electrically conductive coplanarity plate 60 in the form of a ring. This ring may be formed of Delrin® plastic, having an outer diameter of about 39 cm, an inner diameter of about 28 cm, and a thickness of about 6 to 7 mm. The non-electrically conductive annular plate 60 is used to limit the compression of pogo pins 43 a and 44 a to a specified optimum range, such as 60% of the total travel, to assure that all the pogo pins are compressed equally and to assure that there is a coplanar relationship between the tester mother board 40 and the handler board 50.

Guide pins 70 are fixedly mounted on the tester mother board 40 between the rings of spaced tester contacts 41 and 42, and extend toward handler board 50. (Preferably, these guide pins comprise a sleeve threaded in its interior to receive a screw extending upward through mother board 40.) In assembly, matching apertures 51 in the handler board and apertures 72 in the coplanarity plate 60 are guided over guide pins 70, with the plate 60 acting as a stand-off and assuring a predetermined compression of the pogo pins to an optimum compression range for maximum electrical performance, eliminating pin damage due to overstress, and allowing an equal compression of each pogo pin. The addition of permanently mounted guide pins to the tester interface forces a precision alignment between the tester mother board and the device handler board.

Alignment in prior art devices is typically left to outside docking/alignment apparatus which may become misaligned or malfunctioning. Adding this alignment feature to the tester mother board allows for easier detection of errors in the external docking apparatus, docking without the need for external docking apparatus, and the provision for short term manual alignments for experimentation with untried pieces of equipment that may not be mechanically compatible.

FIG. 8 shows a top view of the circular tester mother board 40 with the two rings 43 and 44 of pogo pins near the board periphery. FIG. 8 also shows the inner ring of tester contacts 41 and the outer ring 42. A central aperture 47 in the board allows dry gas to be input for low temperature use. The non-conductive plate 60 extends concentrically between tester contacts 41 and pogo pin rings 43 and 44. Guide pins 70 extend through apertures 61 in plate 60. As shown in FIG. 7, the entire central area W₂ inboard of rings 43 and 44 of pogo pins is available for mounting multiple (e.g. 2 to 8) semiconductor devices on a handler board for simultaneous testing.

FIG. 9 is a more detailed view of a segment of FIG. 8. Pogo pins 44 a and 44 b are electrically connected to tester contacts 41 a and 41 b in inner ring 41 by metallization lines 48 a and 48 b respectively. Pogo pins 44 c and 44 d are connected to tester contacts 42 c and 42 d by metallization lines 48 c and 48 d respectively. Equivalent metallization lines not shown connect other pogo pins to other tester contacts.

Preferably, all metallization lines which connect a tester contact to a pogo pin are laid out to produce the same signal delay. In some embodiments, tester mother board 40 includes four layers of metallization lines, some of which are embedded in tester mother board 40. Because of impedance characteristics, metallization lines which are embedded in mother board 40 conduct signals more slowly than metallization lines on the surface of mother board 40. Therefore, for all metallization lines to have the same delay, interior metallization lines are made shorter than corresponding metallization lines on the surfaces of mother board 40. One can see by inspecting metallization lines 48 a through 48 d that detours have been added to lines 48 c and 48 d to give these lines the same delay as lines 48 a and 48 b. When all metallization lines have the same delay, input signals can be applied to the tester contacts by the tester and output signals detected by the tester without the need to delay some signals with respect to others to assure they arrive at the device under test at the proper time. The absolute delay of a metallization line is easily measured by the tester and subtracted from the test result to determine delays which are introduced by the device under test.

The metallization lines produce a signal delay which may be detrimental to obtaining proper measurement of signals in the device under test. As an advantage of the present invention, placing the pogo pin rings 43 and 44 between tester contact rings 41 and 42 and providing the large work area W₂ on the handler discussed in connection with FIG. 7 means that the total metallization distance from a tester contact to a pin on the device under test may be reduced and the timing accuracy delay correspondingly decreased so that the overall accuracy is increased.

FIGS. 10 and 11 illustrate respective bottom and top surfaces of handler board 50. In FIG. 10, pogo pin contact pads in rings 55 and 56 are connected to vias in rings 53 and 54 which connect to metallization lines in one of the four layers of metallization in handler board 50. For example, contact pad 56 a is connected to via 53 a, which is connected by metallization line 57 to a socket 58 in test site 59. Additional metallization lines not shown connect other vias in rings 53 and 54 to other sockets in test site 59. As discussed above in connection with tester mother board 40, all metallization lines in handler board 50 provide the same signal delay from a contact in ring 55 or 56 to a socket in test site 59. Thus again no adjustment of individual signal timing must take place in order to assure that signals arrive at appropriate times to the device under test which is inserted into test site 59.

FIG. 11 shows part of the top surface of handler board 50. As shown in FIG. 11, via rings 53 and 54 are shown to extend from the bottom surface (FIG. 10) to the top surface (FIG. 11). Some vias in the via rings carry signals from the tester to the test site. For example, via 53 b connects to metallization line 57 b, which connects to contact 58 b in test site 59, which is in turn connected to one of the sockets in the center of test site 59, into which a pin of a device under test is inserted. Each pin of the device under test is connected through appropriate sockets, vias, metallization, and contacts to a pin in the tester. For simplicity, not all connections are shown in the drawings.

The embodiment of FIGS. 8 through 11 includes only a single test site. Other embodiments include additional test sites, as discussed below.

FIG. 12 illustrates the bottom 65 of plate 60 with radial openings 68 extending transversely of the plate from a central cutout 63 to a plate periphery 67. During reduced temperature e.g. 0° C. to −58° C. testing, moisture tends to condense and is undesirable. The side of the handler board into which devices are inserted may be in a cold dry environment and not subject to condensation. However, the back side of some prior art handler boards may be in contact with ambient atmosphere. The cold testing environment soon causes the back side of such a handler board to collect condensation from the atmosphere, which may short together contacts and lines on the back side of the handler board. According to the present invention, condensation is prevented by not only cooling the devices under test with a gas such as nitrogen or dry air, but also surrounding the handler board 50 with dry gas. To apply dry gas to the back side of handler board 50, the gas flows into a central area 62. The dry gas has a dew point of about −100° C., and therefore prevents condensation during testing down to −100° C.

FIGS. 13a and 13 b illustrate side views of alternative embodiments of coplanarity plate 60. As shown in FIG. 13a, grooves 68 a are cut in the bottom of coplanarity plate 60, preferably in a radial pattern, to allow venting of ambient gas as dry gas enters. In FIG. 13b, holes 68 b are drilled through the center of coplanarity plate 60.

FIGS. 14a-14 d show another embodiment of the invention which supports testing of several devices simultaneously.

FIG. 14a shows the top surface of a tester mother board 140. Vias are formed into via groups such as 141, which extend to the bottom surface of board 140 and make contact with correspondingly placed contacts in a tester. The configuration shown in FIG. 14a represents the contact placement which must be used with the SC212 tester from Credence Systems Corporation. Pogo pins are arranged in groups such as 142 and extend upward from the top surface of mother board 140. Most pogo pins are connected through metallization not shown to corresponding vias. Some vias and pogo pins may be ganged together for carrying more current or applying the same signal to more than one pogo pin. Reinforced apertures 143 are provided around the perimeter of mother board 140, and close to pogo pin groups 142 for receiving a shoulder bolt from the handler board and compressing pogo pins in groups 142 against contacts in the corresponding handler board. Guide pins 144 (preferably comprising threaded screws inserted at the bottom side of mother board 140 and held in place by sleeves which form the guide pins) are positioned asymmetrically in mother board 140 and extend upward from mother board 140.

FIG. 14b shows coplanarity ring 146, which is guided into position over mother board 140 by guide apertures 145. Openings 147 receive pogo pin groups 142 (FIG. 14a ) and protect the pogo pins from being bent sideways or excessively compressed. In one embodiment, channels 148 allow ambient air to escape as dry gas is forced into the area. In one embodiment, coplanarity ring 146 has a thickness of 13 mm, which is sufficient that a hole in its side can be used for entry of dry gas during low temperature testing. A thickness range of 5 mm to 20 mm is practical.

FIGS. 14c and 14 d show respectively bottom and top surfaces of a handler board 150 which can be used with tester mother board 140 of FIG. 14a . Handler board 150 is one of many embodiments which can be used with tester mother board 140. Because of the large central area available for test sites, this handler board can hold three devices at one time for testing. Thus a test floor using such a handler board can have three times the throughput of a test floor which must test only one device at one time. Yet no additional floor space is needed for additional testers and handlers (large structures) and no extra expense is incurred in purchasing more of the expensive testers and handlers.

FIG. 14c shows some of the structures provided on the bottom surface of handler board 150. Contact pads in contact pad groups 152 make contact with corresponding pogo pins on mother board 140. Pads in group 152 contact pogo pins in group 142. Reinforced apertures 153 receive the shoulder bolts from handler board 150. When the shoulder bolts are tightened, contacts 152 press against pogo pins 142. Guide apertures 155 receive guide pins 144 from mother board 140 and assure proper alignment of all pogo pins to corresponding contacts. As with other embodiments, metallization lines from contacts in the test area all have the same delay. Metallization lines 157 a, 157 b, and 157 c are shown and are laid out to produce equal delays. FIG. 14c does not show all metallization lines on the bottom surface of handler board 150.

FIGS. 15 through 19b illustrate a linear embodiment of the invention. The mother board is rectangular and the pogo pins are arranged along opposite edges of the mother board. FIG. 15 illustrates a top view of tester mother board 80, and FIG. 16 illustrates coplanarity plate 84. FIGS. 17 and 18 illustrate two cross sections that include tester mother board 80, coplanarity plate 84, and handler board 90. Tester mother board 80 must contact an existing Terradyne Genesis II tester, not shown, through contacts 82 recessed in a rectangular area. Thus, contacts 82 must be positioned to match corresponding contacts in the tester. With this Terradyne tester, tester contacts in a tester mother board must be pressed against the contacts in the Terradyne tester by metal plates 83, which are clamped against the tester. This leaves a small central area through which electrical signals must pass to devices under test.

As shown in FIG. 15, a plurality of tester contacts 82 are provided in the end regions of mother board 80 for cooperating with contacts in the tester. Screws 81 extend upward from mother board 80 for attaching to metal plates 83. In the center portion of FIG. 15, two guide pins 88 a and 88 b provide alignment with coplanarity plate 84 and handler board 90. Reinforced openings 87 receive bolts 86 (FIG. 18) for applying pressure to pogo pins 85 (FIGS. 15 and 17). For simplicity, metallization lines which connect tester contacts 82 to pogo pins 85 are not shown. However, such connections are of course provided. Preferably the metallization lines are laid out to achieve equal delay, as described above.

According to the invention, coplanarity plate 84 not only achieves coplanarity between the tester mother board 80 and the handler board 90 but also allows for long pogo pins (i.e. 1.5 to 1.75 cm) to be safely used to carry the electrical signals out of the recessed area of the tester up to an unrestricted area above the recess.

Inexpensive handler boards of various designs can then be used for testing different numbers of semiconductor devices and different designs of semiconductor devices. Indeed, a board having a cable leading to a probe card for testing unpackaged wafers can be attached by an appropriate handler board to mother board 80.

FIG. 17 illustrates a cross section through structures near the lower edge of FIG. 15. Included in this cross section are screws 81 for firmly attaching metal plates 83 to mother board 80 and pogo pins 85 for carrying signals from the tester contact to handler board 90. After these screws 81 are attached, the combination of metal plates 83 and mother board 80 is clamped firmly against the tester using a clamping means not shown.

FIG. 18 illustrates a cross section through contacts 82, reinforced openings 87 which receive bolts 86, and integrated circuit devices 89, all of which are illustrated in FIG. 15. FIG. 18 also illustrated reinforced openings 91 in handler board 90 for receiving bolts 86.

Coplanarity plate 84, illustrated in top view in FIG. 16 (and suggested by dashed lines in FIG. 15) fits into the central space not occupied by metal plates 83, and includes several openings. Openings 84 a accommodate pogo pins 85. Openings 84 b accommodate some of bolts 87. Other openings 84 c accommodate other bolts 87 and also small integrated circuit devices 89 which modify the test signals. Opening 84 d accommodates other integrated circuit devices for modifying test signals and provides a cavity for flowing dry gas against the bottom surface of handler board 90. Coplanarity plate 84 is guided into position against mother board 80 by guide pins 88 a and 88 b on mother board 80, which fit into apertures 188 a and 188 b, respectively, in coplanarity plate 84. As in other embodiments, the guide pins and openings are positioned asymmetrically so the coplanarity plate and handler board can be fitted against mother board 80 in only one orientation. The relationship between openings in coplanarity plate 84 and structures related to mother board 80 can be seen by inspecting the dashed line representation of coplanarity plate 84 shown in FIG. 15.

As discussed above, pumping dry gas into a cavity 84 d adjacent handler board 90 prevents condensation during cold temperature testing. Also, during high temperature testing of semiconductor devices inserted into handler board 90, dry or ambient gas may be pumped into cavity 84 d to prevent excess heating of mother board 80 and integrated circuit components 89.

When bolts 86 are tightened into position against openings 87 and 91, pogo pins 85 are compressed against contacts on the bottom surface of handler board 90 to make good electrical contact.

FIGS. 19a and 19 b show bottom and top surfaces respectively of handler board 190, which is one embodiment of handler board 90 shown in FIGS. 17 and 18. Contacts 195 which make contact with pogo pins 85 of FIG. 15 are shown in FIG. 19a. Metallization lines connect contacts 195 to respective pins in test sites 194 a through 194 d. For example, FIG. 19a shows that metallization line 193 a connects contact 195 a to pin 192 a in test site 194 a. The embodiment shown in FIGS. 19a and 19 b accommodates four semiconductor devices at test sites 194 a through 194 d for simultaneous testing, and uses half of the contacts 195 in the lower two rows. Some metallization lines in FIG. 19a are not shown because they are located in a metallization layer interior to board 190.

Another embodiment of handler board 90 accommodates eight semiconductor devices each having eight pins, and uses all of contacts 195. Yet another handler board accommodates a single semiconductor device having 64 pins. Clearly many handler boards can be combined with mother board 80 of FIG. 15. Contacts 195 must align with pogo pins 85, guide openings 198 a and 198 b must align with guide pins 88 a and 88 b, and reinforced openings 91 must align with reinforced openings 87 for receiving bolts 86. Dimensions of handler board 90 may vary and metallization lines and test sites may vary. The cost of providing many different handler boards for use with a tester such as the Terradyne tester is considerably less than the cost of providing many mother boards such as mother board 80. And the freedom to vary dimensions in handler board 90 allows one tester such as the Terradyne tester to be used for many more purposes.

FIGS. 20-23 illustrate single boards or parts of single boards for both connecting to a tester and receiving devices to be tested. These structures allow for simultaneous testing of multiple devices by a single tester.

As shown in FIG. 20, the printed circuit board includes multiple metallization layers, in this case, four layers 201-204, separated by three layers of fiberglass or other printed circuit board material. When multiple layer boards are used, it is necessary to make interconnections between the layers, including between layers interior to either surface of the finished board. In FIG. 20, the interconnections are made as the board is being manufactured. A buried via 221 is formed to connect a portion of metallization layer 202 to a portion of metallization layer 203. Vias 222 and 223 respectively connect layer 201 to 202 and 203 to 204. These vias are typically formed by drilling holes into the individual PC board layers before the layers are joined. A single fiberglass board will have metal traces formed on one or both surfaces. The individual layers are then placed in registration with each other and joined, after which the composite board is electroplated, for example with copper, nickel and gold, to make the vias electrically conductive. But with a buried layer such as 221, it is necessary to do the electroplating before all layers are joined since the final joining will bury via 221. Such a construction method is expensive, partly because it is not practical to repair a buried via after completion of the board, but has the advantage that a via for interconnecting two adjacent layers does not interfere with metallization patterns in other layers. For example, metallization traces 203-a and 202-a, and via 221 are all located on the same vertical line as metallization trace 204-a without conflict, and via 223 is located above metallization trace 201-c without conflict.

FIG. 21 shows an alternative structure for interconnecting layers. In the structure of FIG. 21, all layers are formed, drilled with vias and patterned with their respective traces before the layers are joined. After forming and patterning of the PC board layers and joining the layers, the structure is electroplated to form the via connections. With this embodiment, in a location where two traces are to be interconnected, traces are not formed in other metallization layers. In the example of FIG. 21, via 231 connects exterior metallization layers 201 and 204. Via 232 connects interior metallization layers 202 and 203. Via 233 connects exterior metallization layer 201 to interior metallization layer 203.

The structure of FIG. 21 has the advantage of being less expensive and more reliable over long use that the structure of FIG. 20, primarily because it is possible to repair cracks or loose connections in the vias. But this method has the disadvantage that locations where holes will be made and plated must be avoided when laying out metallization patterns in layers not to be connected, and thus the density of interconnection patterns is limited.

FIG. 22 shows an illustrative side view portion of a multi-layer printed circuit board according to the invention, in which an electrical path is provided from a tester contact 41 e to a device pin 24 a. This electrical path may make use of structures illustrated in FIG. 20. In FIG. 22, a metallization trace 201 a formed in metallization layer 201 connects from test pin 41 e to via 222 a, which connects to metallization trace 202 a. Via 221 a connects from trace 202 a to trace 203 a and via 223 a connects from trace 203 a to trace 204 a, which contacts a socket into which pin 24 a extends. Note that device 24-1 is located directly above tester contact 41 e, and yet there is no electrical contact or conflict. In order to avoid obscuring the figure, only the single path is shown. However, in an actual device, there will be an electrical path between every device pin to receive or send test signals and a corresponding pin in the tester. The multiple paths are of a length to produce equal signal delays, and may not be equal to the variation in capacitance and resistance of the various paths.

FIG. 23 shows a top view that is illustrative of the invention but is not to scale. FIG. 23 shows six paths 231 through 236 from test sockets in test site 244. Paths 233 and 234 are deliberately lengthened to produce the desired delay. Paths 231 and 232 are shown to cross each other, an allowable arrangement due to the fact that the paths are in different metallization layers and do not electrically contact each other. The advantage of the invention can be seen in FIG. 23. The radially arranged test pins 31, which extend from the lower surface of board 230 can be directly below portions of the test sites 241 through 244 because of the multiple layers in the board. If the paths are grouped to run from tester pins in one quadrant to a test site in that quadrant and the tester is instructed to apply test signals such that they all go to a nearby device under test, the paths can be made shorter and therefore faster than if there were only a single device to be tested located in the center of the board. Thus the invention accomplishes two goals: higher speed test signal switching, and more devices being tested at one time.

The above description of embodiments of this invention is intended to be illustrative and not limiting. Other embodiments of this invention will be obvious to those skilled in the art in view of the above disclosure. 

What is claimed is:
 1. A method for testing semiconductor devices comprising the steps of: assembling a tester mother board having a plurality of spring biased pins a handler board having a top side and a bottom side, and a coplanarity plate between the bottom side of the handler board and the tester mother board such that the spring-biased pins extending from the mother board are compressed against contact pads formed on the handler board, the coplanarity plate forming a tight joint to both the mother board and the bottom side of the handler board, forming a central hollow region, and having at least two openings by which gas can be introduced to the hollow region and be discharged, attaching to a test site located on the top side of the handler board an integrated circuit device to be tested, wherein the handler board includes metallization lines connecting from the contact pads to the test site; cooling the integrated circuit device to a temperature at which the integrated circuit device is to be tested; and applying a dry gas to one of the openings of the coplanarity plate, thereby introducing the dry gas to the hollow region.
 2. A method for testing semiconductor devices as in claim 1 wherein the flow of dry gas is sufficient to maintain dry gas in the hollow region formed by the coplanarity plate.
 3. A method for testing semiconductor devices comprising the steps of: assembling a tester mother board having a plurality of spring biased pins, a handler board having a top side and a bottom side, and a coplanarity plate between the bottom side of the handler board and the tester mother board such that the spring-biased pins extending from the mother board are compressed against contact pads formed on the handler board, the coplanarity plate forming a tight joint to both the mother board and the bottom side of the handler board, forming a central hollow region, and having at least two openings by which gas can be introduced to the hollow region and be discharged, attaching to a test site located on the top side of the handler board an integrated circuit device to be tested, wherein the handler board includes metallization lines connecting from the contact pads to the test site; heating the integrated circuit device to a temperature at which the integrated circuit device is to be tested; and applying a dry gas to one of the openings of the coplanarity plate, thereby introducing the dry gas to the hollow region.
 4. The method according to claim 1, further comprising transmitting test signals to the integrated circuit device to be tested via the spring-biased pins provided on the mother board.
 5. The method according to claim 3, further comprising transmitting test signals to the integrated circuit device to be tested via the spring-biased pins provided on the mother board. 